1. Field of the Invention
The present invention relates to a wireless power transmitting apparatus, and more particularly, to a wireless power transmitting apparatus for transmitting power from a power emitting device to a power receiving device.
2. Description of the Prior Art
For electronic products charged by combining devices including conventional wires and transformers, power of the electronic products may merely be transmitted by using specific apparatuses fitting specifications of the electronic products. Therefore, while a user buys a power-consuming electronic product, he or she has to buy charging devices corresponding to the bought power-consuming electronic product for serving as media of transmitting power, and it indicates significant inconveniences for the user. For accommodating such a user in charging the bought electronic product, some wireless power transmitting technologies come out.
Primary existing wireless power transmitting technologies are implemented with inductance coils or radio wave propagation. While the wireless power transmitting technologies are implemented with inductance coils, power are transmitted by low-frequency transformation between magnetic energy and electric power; however, only a significantly small amount of power may reach the inductance coils as receiving power, and it indicates that most of power dissipates in the air while the distance between the inductance coils for power transmission increases. Besides, since a transmitting frequency of the inductance coils is usually inconsistent with a receiving frequency of an electronic product for receiving power transmitted from said inductance coils, additional inductance coils having a consistent receiving frequency with the transmitting frequency of the inductance coils for transmitting power have to be disposed within the electronic product for power transmissions. However, the popular electronic products are usually required to possess small weight and compact size, and the inductance coils fail in meeting requirements of a qualified power transmission ratio, locations on the electronic products for the inductance coils are thus limited significantly.
Wireless power transmitting technologies implemented with radio wave propagation, for example, the technology of radio frequency identification (RFID), transmit power with the aid of low-frequency inductance coils or high-frequency wave beams, where power transmission using the low-frequency inductance coils in the wireless power transmitting technologies is the same with power transmission related to inductance coils mentioned above. The high-frequency wave beams for transmitting power carry power to an electronic product located a couple of meters away and equipped with power receiving circuits. However, a supposition, under which the power receiving device is located at an unknown location, has to be followed while the high-frequency wave beams are used for carrying power, an emitting antenna is required to emit electromagnetic beams to whole surroundings so that the power receiving device, which is included by the electronic product, can receive the carried power of the electromagnetic beams. In other words, the emitting antenna has to emit power to omni-direction so that the electronic product is able to receive required power. While an emitting antenna having high directivity is used for emitting the abovementioned high-frequency wave beams, the electronic product is able to receive power with a high efficiency; however, it is also getting expensive in designing the receiving circuit of the electronic product, and feasible locations of the electronic product for receiving the emitted power also meet more limitations.
Please refer to FIG. 1 and FIG. 2, both of which illustrate a resistive surface disclosed in US Patent Publication No. 2007/0139294. While the disclosed resistive surface is used on a housing of a wireless power transmitting apparatus, power transmitted from the emitting antenna may be effectively restricted within a specific space. As shown in FIG. 1, a plurality of electrically conductive plates 318, a plurality of capacitors 320, a plurality of conductive via 322 and 332, an electrode 326, and a dielectric 328 together form a high impedance surface, where necessary discharges are performed with a conductive via 322 between each electrically conductive plate 318 and a corresponding capacitor 320. As shown in the top view of FIG. 2, on the high impedance surface 300, high impedance is generated by both the capacitor 320 and the inductor 330 of each the electrically conductive plate 318 for preventing electromagnetic power from dissipating. Note that the conductive via 322 is disposed at a center of the inductor 330. However, the high impedance surface 300 has to be implemented with large amounts of conductive via 322 and 332 so as to bring a larger volume and an expensive fabrication cost of the wireless transmitting apparatus having the housing the high impedance surface 300.